ALL five killed when a whale-watching boat sank off coast of western Canada were British.

The development came as officials were "urgently" checking with Canadian authorities whether any Britons are among 27 people on board a whale-watching boat which sank, killing at least five people.

The Foreign Secretary has confirmed five Britons were killed.

The boat operated by Jamie's Whaling Station, a local tour company, got into difficulty off the coast of British Columbia on Sunday afternoon local time.

A major search and rescue operation was launched, with the boat partly submerged eight nautical miles from Tofino, on Vancouver Island, according to reports.

Foreign Secretary Philip Hammond said: "It is with deep sadness that I can confirm five British nationals have lost their lives when the whale watching boat they were on sank off Western Canada on Sunday.

"My thoughts are with the family and friends of all those affected by this terrible accident."

He said consular staff in British Columbia were supporting the family members of those who have died and were in close contact with the Canadian authorities.

Earlier a spokesman for the Foreign Office said: "Following the incident in Tofino on October 25, we are urgently seeking information from the local authorities and stand ready to provide consular support to any British nationals involved."

Lt Commander Desmond James of the Joint Rescue Co-ordination Centre said the military agency's search had concluded with five people dead, 21 rescued and one person missing.

It was a clear and sunny day when the 20-metre Leviathan II, operated by Jamie's Whaling Station, made a mayday call late on Sunday afternoon, local time, in the tourist community which is a popular destination for whale watchers on the country's west coast.

John Forde, who runs The Whale Centre, another whale-watching operation, said he did not know how the boat could have sunk.

"Over the course of a season and years we take out thousands and thousands of people on these trips in conditions similar today. I have no idea what the issue was or what actually happened," he said.

Jamie's Whaling Station was one of the first of its kind off Vancouver Island and had been around for many years, Mr Forde said.

In a statement on the Jamie's Whaling Station website, owner Jamie Bray wrote: "It has been a tragic day. Our entire team is heartbroken over this incident and our hearts go out to the families, friends and loved ones of everyone involved.

"We are doing everything we can to assist our passengers and staff through this difficult time.

"We are co-operating with investigators to determine exactly what happened.

"In the meantime, we want to extend our most sincere thank you to the first responders, rescue personnel, and everyone from Tofino and the local First Nations communities who assisted with the response efforts.

"We will provide further updates when information becomes available."